The comfort and safety provided by a headrest of a seat is largely achieved by a proper position of the headrest relative to the head of a user of the seat. Techniques have been developed for adjusting not only the height but also the front-back position of the headrest with headrest pillars (see, for example, Patent Documents 1 and 2).
The headrest disclosed in Patent Document 1 includes a ratchet. The ratchet has gear teeth and works as an engaged member. A locking member is engaged stepwise with any of the gear teeth. These structures enable the front-back position of the headrest to be gradually adjusted to enhance the comfort and safety of the seat user.
The headrest disclosed in Patent Document 2 includes right and left pairs of X-links. These links are pivotally coupled about a link shaft (shaft) to adjust the front-back position of the headrest.